I just finished Disco Elysium, and, like some around here, I think it is as good as Planescape: Torment, and that it is the first game to be directly descended from it. It's true that Age of Decadence, in its talking path, does something that resembles it, but its ancestry is clearly Fallout. Some scenes are splendid —the karaoke, the one going to the island by boat with the boombox playing, the dream about the ex-partner, etc.—. The writing, the created world and some of the characters also seemed very well done.
That said, I agree that the weakest part is the killer at the end. He is clearly a deus ex machina. Especially in a police story, it should not happen that the murderer appears only by the end, even though, as has been shown in some images, there are clues that, in a second play, can be interpreted as if they were pointing to him. I think one way this problem could have been avoided is if the killer had been placed somewhere prior to where Harry meets him; after all, the killer says he goes everywhere and is seen by everyone. Maybe he could have been listed as a possible suspect, later ruled out, or just a chance encounter.
Another issue that I think would have made it a better game is if some skill checks had been higher. I've been through several that, had I failed them, would have made me want to replay it by molding a different Harry. And, also in relation to the skill checks, I liked that on some occasions the skill would simply have a possibility of response, but it did not tell you which was the optimal one. Everything should have been like that, and it would have been better too that, once an option was elected, the other ones were eliminated. This way, I think, the gameplay would have felt a little less passive and more dynamic. Because DE shows that basing the gameplay mainly (the exploration should also be considered, although I wish there were more places) on conversations and skill checks tends to make the gameplay a bit monotonous, although it manages to save the situation due to its quality in others elements.
In any case, a really good game, and hopefully ZA / UM will be encouraged to delve into its design and created world in their next game. Also, I would like to see more detectives games.
